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FreeBSD-EN-20:16.vmx                                            Errata Notice
                                                          The FreeBSD Project

Topic:          vmx driver packet loss and degraded performance

Category:       core
Module:         vmx
Announced:      2020-08-05
Affects:        FreeBSD 12.1
Corrected:      2020-01-20 22:15:33 UTC (stable/12, 12.1-STABLE)
                2020-08-05 17:09:54 UTC (releng/12.1, 12.1-RELEASE-p8)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

vmx(4) is a driver for the virtualized network interface device used by
VMware.  It implements TCP segmentation offload (TSO), a performance
feature which allows the device to perform TCP segmentation immediately
prior to packet transmission, reducing the amount of work required of
the kernel's TCP implementation.

II.  Problem Description

vmx(4) in FreeBSD 12.1 contains a bug which causes the driver to set up
transmit descriptors incorrectly when performing TSO.

III. Impact

With TSO enabled in vmx(4) interfaces, TCP sessions may hang or
experience degraded performance due to packet loss.

IV.  Workaround

Using ifconfig(8), TSO can be disabled on vmx(4) interfaces by
specifying "-tso".

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for errata update"

2) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-20:16/vmx.patch
# fetch https://security.FreeBSD.org/patches/EN-20:16/vmx.patch.asc
# gpg --verify vmx.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r356932
releng/12.1/                                                      r363920
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236999>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-20:16.vmx.asc>
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